Current and historical procedures for the treatment of colon and rectal cancer have been based upon the natural history of tumor spread, and thence, upon operative and non-operative options. Operative options generally have looked to the physical location and surgical resection of tumor. A variety of techniques have been brought to bear in the art with the purpose of aiding the surgeon in detecting and localizing neoplastic tissue as part of this surgical procedure. ("Neoplastic tissue", for present purposes, often is referred to as cancerous tissue, though malignant tumor and malignant tumor cells also are found in the terminology of the art. The term "neoplastic tissue" includes all of these.) A substantial amount of effort in aiding the surgeon in locating neoplastic tissue has been through the utilization of radiolabeled antibody for detection purposes. For example, one technique includes the scintillation scanning of patients injected with relatively high energy, e.g. .sup.131 I labeled antibodies. Such photoscanning or scintillation scanning provides scintigrams difficult to interpret or of little value for detection of small lesions because of blood pool background radioactivity. Computer subtraction of radioactive blood pool agents and the use of two labeled antibodies (one specific for the tumor and one non-specific) have been attempted to enhance imaging. Nevertheless, such techniques have been found to provide little, if any, useful information to the surgeon, especially over and above CAT scans, magnetic resonance imagings, and like traditional techniques. Typically, large tumor is readily located by the surgeon by visualization at the operating theater as well as through palpation, i.e. the feel of a tumor as opposed to that of normal tissue. To achieve operative success, however, it is necessary for the surgeon to somehow locate neoplastic tissue at positions within the body cavity not accessible with vision, for example internally within the pelvic region or behind the liver or pancreas. It also is necessary for the surgeon to locate "occult" tumor at any position. Occult tumor or occult neoplastic tissue is that which is so dimunitive in size as to be unidentifiable either by sight or feel. Failure to locate and remove such occult and non-visible tumors generally will result in the continued growth of cancer in the patient, a condition often misidentified as "recurrent" cancer. In general, conventional diagnostic techniques as, for example, use of the classic gamma camera and the like, fail to find or locate occult tumor. As tumor sites become smaller, the radionucleide concentrations at a given tumor site will tend to be lost, from an imaging standpoint, in the background radiation necessarily present.
U.S. Pat. No. 4,782,840 by Martin, M.D. and Thurston, Ph.D., entitled "Method for Locating, Differentiating, and Removing Neoplasms", issued Nov. 8, 1988 (the disclosure of which is expressly incorporated herein by reference) reviews such scintillation scanning technique and discloses a much improved method for locating, differentiating, and removing neoplasms. Such technique utilizes a radiolabeled antibody and a portable radiation detection probe which the surgeon may use intraoperatively in order to detect sites of radioactivity. Because of the proximity of the detection probe to the labeled antibody, the faint radiation emanating from neoplastic tissue at occult sites becomes detectable, for example, in part because of the inherent application of the approximate inverse square law of radiation propagation. The procedure is known as the Radioimmunoguided Surgery.TM. system (Radioimmunoguided Surgery being a trademark of Neoprobe Corporation, Columbus, Ohio) and is successful additionally because of a recognition that tumor detection should be delayed until the blood pool background of circulating radiolabeled antibody has had an opportunity to be cleared from the body. As a consequence, the photon emissions or radiation emitted by minor tumors compared to surrounding tissue becomes detectable in view of the proximity of the probe device to it. Fortuitously, the '840 patent discloses the ability of the radiolabeled antibody to remain bound to or associated with neoplastic tissue for extended periods of time with the radio tag still bound thereto. Moreover, even though the accretion of radioactivity at the tumor site decreases over time, the blood pool background and surrounding tissue (relative to the tumor sites) decrease at a much greater rate so that the radioactive sites can be determined readily utilizing a hand held probe positioned in close proximity with the tissue under investigation. Also discussed in the '840 patent is the improved inventive methodology focused upon lower level energy isotopes exhibiting photon emissions of energy levels less than about 300 Kev advantageously and, preferably, less than about 150 Kev.
The instrumentation developed to support the radioimmunoguided surgery system has been called upon to meet rigorous performance criteria. Radiation emitted from occult tumor necessarily is very sparse and will emit to evoke a relatively low count rate upon detection. This low count rate, in turn, is developed with a corresponding count rate from the same radioisotope which is background radiation, albeit in itself low, but which must be accommodated for. The circuitry involved for such instrumentation is described, for example, in U.S. Pat. No. 4,801,803 by Denen, et al., entitled "Detector and Localizer for Low Energy Radiation Emissions", issued Jan. 31, 1989. To evaluate detected emissions and the counts generated therefrom with the instrumentation, a microprocessor-driven control program has been developed as is described in U.S. Pat. No. 4,889,991, by Ramsey, et al., entitled "Gamma Radiation Detector with Enhanced Signal Treatment", issued Dec. 26, 1989.
This instrumentation supporting the probe device which is held by the surgeon and maneuvered within the body cavity is retained within a battery-powered console located within the operating room. Because of the low levels of signal evoked at the crystal detector within the probe, that device itself carries a preamplification stage for the purpose of generating a signal output suitable for transmission by cable or the like to the adjacent console. The preamplification stage performs in conjunction with a cadmium telluride crystal detector, and this combination of components is called upon to perform at the temperatures of the human body while undergoing calibration at substantially cooler temperatures found, for example, in the operating room environment. This requirement has tended to reduce the energy level discrimination flexibility of the devices. The architecture of the hand-held probe, particularly as it is concerned with the noise-free mounting of the cadmium telluride crystal, has been described, for example, in the noted U.S. Pat. Nos. 4,801,803, 4,893,013, by Denen, entitled "Detector and Localizer for Low Energy Radiation Emissions", issued Jan. 9, 1990, and in U.S. Pat. No. 5,070,878, by Denen, entitled "Detector and Localizer for Low Energy Radiation Emissions", issued Dec. 10, 1991. The probe so described has an overall length of about 15 cm; is tubular in cross section, and has a forward tip portion canted at an angle of about 30.degree. to aid the surgeon in maneuvering it within the body cavity. Where such maneuvering requires access to tissue adjacent the pelvis or behind the liver or pancreas, even this relatively small hand-held probe may become difficult for the surgeon to position as desired. Once the surgeon has located neoplastic tissue at these hidden locales, it may be desirable then to use the remaining available perception of feel for the purpose of additional verification of a tumor site. However, where the hand is called upon to grasp the tubular handle component of the probe, this surgical exercise may become difficult.